No. Information and images taken by Hubble Space Telescope are not withheld,
but they do take time to get to the public.

Many of the images taken by Hubble are never formally released to the public
because they are typically only of interest to the scientific community. Full
access to these data, which can be processed into viewable images, is available
online via the Hubble Data Archive.
The archive's mission is to serve the scientific community. It may not be
useful to or easily operated by the general user.

Hubble images produced by the Space Telescope Science Institute are covered
by copyright law, as stated on our Web site at http://hubblesite.org/copyright/.
This copyright covers most images displayed on all of our Web sites.

Here is the scoop on why it takes time to get the photos out to the public.

The areas of the sky and the objects that Hubble's various optical and spectrographic
cameras take pictures of are very carefully planned and scheduled. Scientists
from universities and scientific institutions prepare proposals to use the
telescope. If their proposal is accepted, time on the telescope is scheduled.
Once the scientists have their raw data from the telescope, they then have
one year in which to conduct their research and prepare papers. After this
one year, the information becomes available to the public.

Sometimes “Early Release Observations” are released to the public,
as is the case when a new instrument is installed. Photos are then released
as soon as possible after the installation to let the world know that the
camera is performing up to its expectations.

If you would like to see a "scrapbook" of photos, as they look
when they are "translated" from the original digitalized pixels
sent from the instruments aboard the Hubble, you can see them at the MAST
Scrapbook:http://archive.stsci.edu/scrapbook.php

Again, these are photos that have become available after the one-year grace
period for the astronomers.

HubbleSite and STScI are not responsible
for content found outside of hubblesite.org and stsci.edu